Psychiatrists often treat depressed patients who have significant medical illnesses (Wells, et al 1991), the presence of which complicates diagnosis and treatment decisions. The goal of the proposed research is to evaluate and treat depression. The specific aim is to investigate how these practice patterns (e.g. antidepress-ant dosing) are associated with increasing medical illness severity. The proposed study will examine psychiatrist practices with a clinical population of depressed individuals. Four hundred patients newly diagnosed with major depression will complete a structured self-report instrument upon initial evaluation. Practicing psychiatrists will be members of one of three group practices which have significantly different sociocultural and reimbursement characteristics. Psychiatrists will make a structured initial assessment and a trained research assistant will use a structured instrument to assess medical illness severity. Patient follow-up assessments and structured chart review at six months will provide practice pattern data. It is hypothesized that increasing medical comorbidity will be associated with lower antidepressant dosing, increased use of laboratory evaluations, and greater extent of recommendations regarding non-psychiatric medications. The study will also examine the contribution to practice patterns of other variables including physician uncertainty, physician experience, physician's conceptualization of the relationship between depression and the medical condition (e.g. depression due to a medical condition vs. depression co-existing but unrelated to the medical condition), practice location, and patient attitudes regarding depression. Longitudinal data will also be used to determine how medical illness severity predicts practice pattern variation over the course of treatment of depression.